WTP comes with JS Validator which is by default configured to
"Enable JavaScript semantic validation".

Defaults are set somehow but soon
you will have to turn OFF "the whole thing" because:

Optional Semicolon: Ignore
because of Dojo and other framework authors do not care

Local Variable is never read: Ignore
because it does not work, local.member is not considered reading local by WTP

Uninitialized local variables: Ignore
This is just JS style of me and many others

And after turning this all OFF, you will end up with
Type mismatch: cannot convert from any[] to any ItemFileWriteStore.js /dojo/data JavaScript Problem line 581
on simple lines like: var serializableArray = [];

Since this warning cannot be turned off (no UI item for this),
you must modify the plugin
or just turn WHOLE "SEMANTICS VALIDATOR" OFF.

Another piece of code that is useless, thanx for wasting my time again.

see also:
http://stackoverflow.com/questions/5765955/javascript-array-why-is-this-not-valid

Update:
Eclipse IDE for JavaScript Web Developers
eclipse-javascript-indigo-SR1-macosx-cocoa-x86_64.tar.gz
contains quite old version of the plugin:
plugin version org.eclipse.wst.jsdt.core_1.1.101.v201108151912.jar

Some ideas and wishes
from my own unfinished code performing "page analysis".
My code is not only performance based so some may not aplly to DOM Monster.

Inline Scripts Detection

Standard vs. Quircks mode

Empty ULs and others that cannot be empty (semantics)

Meta tag "best pracices"

Anti-SEO hunter (bad, old SEO practices detection)

jSession string and other identifiers in URLs

Accessibility checks

DHTML event registration

Ajax style links (# fragment links)

.... more and more

So my bookmarklet is/was mix and
I'm thinking (thanx to @souders)
about splitting it into more categories now
and maybe "reuse" existing code or whole bookmarklet,
once they will comply with minimal "js qualities" ;-)